 One of the key parts of the scientific method is the ability to make measurements.  If I told you a measurement was What would be your response?

 The metric system is the one used in science. The units are called SI units-we will see that not all the units we will use are SI units.  SI base units are listed on p 34.

QuantityUnitSymbol  lengthmeter m  masskilogram kg  timesecond s  currentampere A  temperatureKelvin K  amt. substancemole mol 3

NameSymbolMultiplier  mega M 10 6  kilo k 10 3  deka da 10  deci d  centi c

NameSymbolMultiplier  milli m  micro   nano n  pico p  femto f

 You must know the following SI prefixes:  Kilo-1000  Deci-0.1  Centi 0.01  Milli  Others will be provided.

Common Conversion Factors  Length ◦ 1 m = inches ◦ 2.54 cm = 1 inch  Volume ◦ 1 liter = 1.06 qt ◦ 1 qt = liter 7

 The SI base units are used to derive other units. Some are listed on page 36. One of the common derived units is volume. The SI unit for volume is the cubic meter (V=lxwxh) m 3.  This is not a very practical unit to use in the lab.

 The most commonly used metric units for volume are the liter (L) and the milliliter (mL). □ A liter is a cube 1 dm long on each side. □ A milliliter is a cube 1 cm long on each side.

 One important physical property of matter is density.  Density = mass/volume  Every substance has its own unique density.  See p 38 for a list.

 There is some interesting info in the table.  Notice the density of ice: 0.92g/cm 3  and for water 0.998g/mL  What do you think this means?

 Since the density formula has 3 variables, 3 types of problems are possible.  D = m/V

 1. given mass and volume-find density  a substance has a mass of 23.2 grams and a volume of 18.5 cm 3. Find its density.  2. given density and volume, find mass (g)  D = m/V so m=D x V  The density of silver is 10.5 g/cm 3. Find the mass of a block of silver with a volume of 40.0cm 3.

 3. Given the density and mass, find the volume of a substance.  D= m/V so V= m/D  Find the volume of a piece of iron that has a mass of 147grams. ( density of iron = 7.86 g/cm 3 )

 It is important to be able to convert one unit to another. We will make use of conversion factors (also known as unit factors). For example: how many grams are there in 25 kg?  What you need to know is how many grams there are in 1 kg. We know (or will know) that there are 1000g in one Kg (or 1 kg contains 1000 grams.

 25 kg. X 1000 g = g. 1 kg

 Some for you to try:  a g to kg  b cm to m  c mg to kg

 Accuracy refers to the proximity of a measurement to the true value of a quantity.  Precision refers to the proximity of several measurements to each other.

 If we happen to know the true or accepted value for a measurement then we can calculate the per cent error in our measurement.  Percent error = (measured value-accepted value) X 100  accepted value

 Every measurement has some uncertainty associated with it. See page 46. In every measurement there is a known or certain quantity and an estimated quantity.  In every measurement all the numbers are significant.

 Many measuring instruments allow us to make an estimate of the last number in a measurement.

 Piece of Black Paper – with rulers beside the edges 22

 Piece of Paper Side B – enlarged ◦ How long is the paper to the best of your ability to measure it? 23

 Piece of Paper Side A – enlarged ◦ How wide is the paper to the best of your ability to measure it? 24

 Exact numbers ◦ 1 dozen = 12 things for example  Accuracy ◦ how closely measured values agree with the correct value  Precision ◦ how closely individual measurements agree with each other 25

 Significant figures ◦ digits believed to be correct by the person making the measurement ◦ If you measured it-it’s significant  Exact numbers have an infinite number of significant figures = 1 dozen because it is an exact number 26

Significant Figures - Rules  Leading zeroes are never significant has three significant figures  Trailing zeroes may be significant must specify significance by how the number is written 1300 nails - counted or weighed?  Use scientific notation to remove doubt 2.40 x 10 3 has ? significant figures 27

 Try these:  How many significant figures are present in each of the following measurements  g ______  20.4 cm _____  970 bricks _____  kg ____  miles ______

 Multiplication & Division rule Easier of the two rules Product has the smallest number of significant figures of multipliers 29

 Multiplication & Division rule Easier of the two rules Product has the smallest number of significant figures of multipliers 30

 Multiplication & Division rule Easier of the two rules Product has the smallest number of significant figures of multipliers 31

 Addition & Subtraction rule More subtle than the multiplication rule Answer contains smallest decimal place of the addends. 32

 Addition & Subtraction rule More subtle than the multiplication rule Answer contains smallest decimal place of the addends. 33